Effects Of Ru-doping On Structures And Properties Of Vanadium Oxide Thin Films

Because vanadium dioxide has the semiconductor-to-metal phase transition with the transition temperature at 68°C,it has been extensively studied in smart windows,photoelectric switches,storages and uncooled infrared detectors.Due to the characteristics of phase transition temperature and phase transition hysteresis,the application of VO₂ in practical devices has some limitations.As an effective way to change the structure and properties of VO₂,doping has been reported by many researchers.In this dissertation,we investigated the effects of Ru doping on VO₂ thin films with different Ru contents,different substrate temperatures,and Ti-Ru co-doping elements by means of magnetron sputtering.Through XRD,Raman,XPS（EDS）,SEM,AFM analysis and other characterization to explore the films^’composition,surface morphology,and crystal structure.Using the four-probe and step-tester to test the resistivity-temperature phase transition characteristics of the thin films to study the regulation and mechanism of the phase transition of VO₂ doped with Ru and Ti-Ru co-doping.（1）The effects of doped Ru on the microstructure and properties of vanadium dioxide were studied.The results of characterization analysis show that the Ru-doped VO₂ thin films still maintain the M-phase structure and the crystallite size decreases;Ru is present in the thin films in the form of+4 valence,Ru-doping can alleviate the spontaneous oxidation of VO₂ in air;Ru-doping inhibits the growth of particles and reduces the surface roughness.When 1at%Ru is doped,the phase transition temperature reduces by 10.5^oC,Ru⁴⁺ions are remarkably better than other tetravalent dopants for reducing the T_SMT of VO₂.The addition of Ru significantly increases the temperature coefficient of resistance（TCR）and lowers the resistivity of the films at room temperature.The TCR of the VOR-4 thin film doped with 2.32 at%Ru is as high as 4.82%/℃and the resistivity is only 0.63Ω·cm.It provides a new method for the preparation of VO₂ films with low T_SMT,low resistivity,high TCR.（2）Based on the study of phase transition characteristics of Ru-doped vanadium dioxide,the influence of different substrate temperatures on the microstructure and properties of Ru-doped vanadium dioxide was further studied.The increase of substrate temperature will weaken the phase transition characteristic of Ru-doped vanadium oxide films and decrease the temperature coefficient of resistance（TCR）,When the substrate temperature is higher than 150^oC,the Ru-doped vanadium oxide thin film has the resistivity of the metal film and the phase transition characteristics were completely suppressed.So the TCR was significantly reduced.The increase of substrate temperature significantly reduced the grain size but did not affect the M-phase structure of the films.（3）The effects of Ti-Ru co-doping vanadium dioxide were studied on the microstructure and properties.The Ti-Ru co-doping VO₂ films reduce the grain size without changing the monoclinic character.Ti and Ru are present in the film sample in the form of+4 valence.Ti-Ru co-doping VO₂ suppresses grain growth on the surface of the film,making the film surface density better.The effects of Ti and Ru doping on the phase transition characteristics of VO₂ films are independent.Doping with Ti inhibits the phase transition properties of the films.Doping with Ru reduces the resistivity of the film at room temperature and the Ti-Ru co-doping VO₂ makes the film obtainable,TCR higher and stable over temperature range.It provides a new method for the preparation of VO₂ films with low resistivity,no phase transition,and high TCR for uncooled infrared detectors.